Measurement of back-bombardment temperature rise in microwave thermionic electron guns.

We describe a simple method to measure the back-bombardment heating temperature rise as a function of time in pulsed microwave thermionic guns using a fast rise-time InGaAs detector and optical pyrometer. Gaining knowledge of the nature of that temperature rise and the corresponding current out of the gun are the first steps in devising a scheme to counteract the back-bombardment heating which lengthens the micropulses, limits the macropulse length, and increases the energy spread of the emitted electron beam. We measured a temperature rise of 59 K in our LaB6 cathode which delivered a peak of 600 mA over a 5 μs RF pulse in our 0.

Electron bunch energy and phase feed-forward stabilization system for the Mark V RF-linac free-electron laser.

An amplitude and phase compensation system has been developed and tested at the University of Hawai'i for the optimization of the RF drive system to the Mark V free-electron laser. Temporal uniformity of the RF drive is essential to the generation of an electron beam suitable for optimal free-electron laser performance and the operation of an inverse Compton scattering x-ray source. The design of the RF measurement and compensation system is described in detail and the results of RF phase compensation are presented.

Remote Raman spectra of benzene obtained from 217 meters using a single 532 nm laser pulse.

This report describes a mobile Raman lidar system that has been developed for spectral measurements of samples located remotely at ranges of hundreds of meters. The performance of this system has been quantitatively verified in a lidar calibration experiment using a hard target of standardized reflectance. A new record in detection range was achieved for remote Raman systems using 532 nm laser excitation.

Observation of sub-Poisson fluctuations in the intensity of the seventh coherent spontaneous harmonic emitted by a rf linac free-electron laser.

We report the observation of sub-Poisson intensity fluctuations in the coherent spontaneous harmonic radiation generated by an infrared free-electron laser in a photon counting experiment using a well-defined ensemble of electron pulses. These observations constitute the first observation of a nonclassical state of the radiation field generated by a beam of free electrons. The fluctuations observed in the experiment are smaller than those expected from semiclassical radiation theory, and larger than those expected from electron shot noise.

Observation of a cw dark-field signal in an absorption spectroscopic experiment using a phase locked free-electron laser.

We introduce a technique for ultrasensitive absorption spectroscopy using the GHz-rate pulse train from a phase-locked free-electron laser (FEL), in which the fractional power absorbed from one or more laser lines reappears as a signal on the dark background between the pulses emerging from the sample. Preliminary absorption experiments in 15 Torr cm of methane at 3.25 &mgr;m, using phase-locked pulses from the Mark III FEL, clearly reveal an interpulse beat signal due to absorption by adjacent molecular rotational lines which is generated only in the presence of interpulse phase coherence.

The Compton backscattering process and radiotherapy.

Radiotherapy utilizes photons for treating cancer. Historically these photons have been produced by the bremsstrahlung process. In this paper we introduce Compton backscattering as an alternate method of photon production for cancer treatment.

Fourth-harmonic generation in a single lithium niobate-crystal with cascaded second-harmonic generation.

Tunable second- and fourth-harmonic radiation was generated in a single 1-cm-long lithium niobate (LiNbO(3)) crystal with the Mark III infrared free electron laser at Duke University. The fundamental laser radiation was tuned from 2 to 2.5 µm, yielding 1-1.

Cavity dumping for free electron lasers.

The cavity dumping technique, applied to free electron lasers (FEL), is described. Taking advantage of both numerical simulations and experimental results on the Mark III FEL, a fairly exhaustive analysis is reported. In particular, we show that the output peak power can be increased by a factor even higher than one hundred.

Mode characterization, autocorrelation measurements, and harmonic conversion with pico- and femtosecond pulses delivered by the Mark III free-electron laser.

After briefly reporting on the present status of the infrared free-electron laser now operating at the Stanford Photon Research Laboratory and powered by the linear accelerator Mark III, we discuss the results of using nonlinear optical techniques for both the characterization of its output radiation and the enhancment of its tunability range. In particular, to show the evidence of possible self-guiding effects, a new and reliable technique has been devised and successfully tested for real-time monitoring of the micropulse evolution during the buildup of radiation. Finally, we discuss the main problems connected with the damage threshold of optical materials.

Acoustooptical suppression of sideband instabilities in free electron lasers.

We describe an electronically tunable intracavity filter, based on the acoustooptic effect, that suppresses the sideband instabilities in a free electron laser. Different configurations are analyzed, and the problems encountered in the design and construction of a broadband acoustic transducer are discussed in some detail. In addition, some preliminary experimental results on the construction of broadband acoustic transducers are reported.

Tunable electrooptic intracavity filter for sideband suppression in free electron lasers.

We describe a tunable intracavity filter, which, taking advantage on the electrooptic effect, limits the growth of the sidebands in a free electron laser and even suppresses them in some cases.

Superconducting helically wound magnet for the free-electron laser.

Theoretical and experimental studies conducted by the Stanford Free Electron Laser group have resulted in the first operation of a free-electron laser amplifier and free-electron laser oscillator. Two superconducting helically wound periodic magnetics have been constructed for use with the laser. In this paper we present a discussion of design considerations and test results for the two magnets.